I have a pet hypothesis that, on average, those into step porn are more likely not have grown up with a sibling of the gender they fancy. I reckon those of us who did are more likely to repelled by anything alluding to incest.
People who grew up with ACTUAL hot step siblings notwithstanding.
But isn’t their fake incest porn anyway? I know it at least used to exist, so I don’t think it’s illegal to make that, so clearly that means that there isn’t a big market for it.
My theory has always been that it’s a way to trick peoples minds that the actors are younger, because that very much is a thing.
I don’t know anyone who is attracted to their siblings, even if they are conventionally very attractive.
If my memory serves, in the early days of free online porn the step-prefix wasn’t generally used. I can dimly remember the time it started appearing all over and I always suspected it was because implying it was actual incest was a bit too taboo so they modified the titles into step-porn so that it’s not as provocative. Maybe advertisers had something to do with it, who knows. Or maybe it’s because they realized that people find it easier to fantasize about step-siblings rather than biological ones.
You make some good points, there could be a lot of factors… hell it could be that it took a while for the divorce and remarry rate to kick up and before that step siblings simply weren’t as common. There should probably be a good lag too between those numbers and when it started to become a cultural thing.
I would be interested in some deep research at this point.